Garden Pests and Diseases: Sick Astrophytum, 1 by dave2889

dave2889 wrote:
Apologies for taking so long to respond.

I unpotted the cactus to check the roots and to help dry it out as suggested, the roots seem OK, and the brown area is firm, not soft as I’d expect with root rot. What other diseases would cause the flesh to turn this colour? Is it worth trying to save the cactus, or will any efforts end up being futile? I've uploaded another image that shows the bottom of the cactus better than the last 3.